1. Field of the Invention
The present invention relates to an improvement in an electrophotographic image forming apparatus that uses a dry two-component developing method and, more specifically, to an image forming apparatus that allows high-value added printing using, for example, transparent toner.
2. Description of the Related Art
In the industrial field of conventional image forming apparatus, the majority of demand is from offices and SOHOs (Small Office/Home Office). Therefore, technological development has been made to satisfy the demand from offices and SOHOs, such as a reduction in installation area, a reduction in downtime, or improvement in usability. However, in recent image forming apparatuses, high-value added printing becomes increasingly popular because, for example, various image forming apparatus that can use transparent toner have been available on the market. Therefore, in the industrial field of image forming apparatus, the market of production printing in which output materials are used as products is becoming more active. The industrial field of image forming apparatus has been growing in recent years.
As described above, in the industrial field of recent image forming apparatus, high-value added printing becomes increasingly popular. However, the development of conventional image forming apparatus has been directed mainly to the use in offices and SOHOs. Therefore, if the basic platform of the image forming devices included in an image forming apparatus that has been developed before is used to perform high-value added printing, many technical problems will arise. For example, when high-value added printing is performed by using transparent toner, the configuration of image forming stations or the layout of an image forming engine must be significantly changed according to when the transparent toner is used in the procedure of image formation. More specifically, when only one color of transparent toner is added to conventionally and commonly used four basic colors of toner for cyan (C), magenta (M), yellow (Y), and black (K), the image formation layout must be fundamentally changed. Therefore, an image formation engine that can perform high-value added printing by using transparent toner must be newly designed according to an application for use, or the design of an existing image forming apparatus must be greatly changed. To achieve high-value added printing easily at low cost, various problems must be solved.
As an example of the image forming apparatus that can perform high-value added printing, Japanese Patent Application Laid-open No. H8-265583 discloses a color image forming apparatus in which a user can freely select performance with priority given to copy speed or capability of printing black characters with high quality according to the user's preference. In the image forming apparatus according to Japanese Patent Application Laid-open No. H8-265583, an image color recognition unit that allows selection as to whether the formation of a black image is performed first, second, or later is provided to achieve high-value added printing. However, the unit for achieving high-value added printing in the invention disclosed in Japanese Patent Application Laid-open No. H8-265583 is very complicated. Therefore, high-value added printing cannot be achieved without greatly changing the device configuration currently used.
In one known image forming apparatus, the user can replace any one of the image forming stations. In this manner, although an image forming engine provided with, for example, four image forming stations for the four basic colors of toner is used, an image using five or more colors of toner can be formed on a single side of a single recording medium. Therefore, with this image forming apparatus, an image can be formed using toner with a larger number of colors than the number of the image forming stations. In such an image forming apparatus, even though the image forming stations for the four basic colors described above are used, transparent toner and the like can be additionally used relatively easily. However, in this image forming apparatus, a series of operations including forming an image with additional color toner and fixation on a recording medium that has been subjected to fixation must be performed. In this method, a plurality of (two) fixing operations are performed on one image forming surface of a recording medium. Therefore, an amount of heat applied to the recording medium for fixing in image formation has been wasted, and the recording medium has been excessively warped and deformed because an excessively large amount of fixing heat has been supplied to the recording medium and a toner image. In addition, image abnormality such as abnormally high image gloss has occurred.